Thursday, July 17, 2014

Selected Readings on Human Health, Disease, and the Environment

The following
are responses and summaries of various readings related to Human Health,
Disease, and the Environment.

Life Support: Environmental Endocrine Disruption

Chemicals found in the environment
have effects on fetuses much more than on adults because even the slightest of
changes in the hormone levels of the undeveloped human can have very drastic
consequences. These chemicals are able
to directly bind to or block the hormone receptors making gene transcription
initiated by the hormone receptors erroneous.
Similar exposure levels in adults do not show nearly as great
physiological changes. Possible
abnormalities include feminization of males, abnormal sexual behavior, birth
defects, altered sex ratio, lower sperm density, decreased testis size, altered
time to puberty, cancers of the mammary glands or testis, reproductive failure
and thyroid dysfunction. Studies that
have been conducted have difficulty in consistency due to the time between
exposure and the resultant effects, such as cancer showing decades after first
exposure, and finding a control population, since any control population is
going to already have some degree of exposure.
Organochlorine contaminated food has been shown to affect the brain
development of lab animals and children exposed have shown delayed psychomotor
development and increased distractibility.
Some pesticides result in decreased brain density of some nerve receptor
types and hyperactive behavior. Because
hormones act at such low levels even the slightest of chemical exposure can
result in very bad developmental effects.
One of the main failures of past studies is their focus on the
individual rather than the population as a whole, though the size and
seriousness of the health threat is still uncertain. Work by the International Joint Commission,
United States and Canada, has begun striving towards the elimination of
volatile chemicals. They hope for zero
discharge of chemicals from human activities, analysis of chemical effects from
creation to destruction and afterwards, and reversing the burden of proof from
showing that a chemical is harmful to showing that a chemical is not harmful
before it is allowed to be used.

Body Burdens of Industrial Chemicals in the General Population

The United States produces and uses
over 70,000 chemicals and each year over 1500 new chemicals enter the
market. The main problems with these
chemicals is that some of them cannot be processed by the metabolic system of
the human body and therefore collect in the fatty tissues of people. According to studies, the general population
of the US contain nearly 700 different chemical contaminants within their fatty
tissues. Work began in earnest about three
decades ago in assessing the health risks of those exposed either
occupationally or environmentally to chemical contaminants. More recently the National Health and
Nutrition Examination Survey has begun regularly studying the chemicals
contained within our bodies. This survey
will allow for future reports to show how our health is being affected by
environmental exposure. One of the most
important aspects of the survey however is to merely define a control group, or
to show what chemicals are expected to be seen in the general population and to
what degree they should be found. One of
the most detrimental chemicals on our health are organochlorines. Organochlorines hold firmly in our
environment due to the fact that chlorination changes the stability of organic
chemicals. They are also lipophilic,
more soluble in fats than in water, thereby accumulating in fatty tissues. These chemicals affect all species but
carnivores especially. Being at the top
of the food chain humans are especially contaminated due to our high intake of
fat based meats which undoubtedly contain the chemicals. The concentrations of chemicals in the fatty
tissues increase with age and therefore the elderly hold a much greater
concentration than the middle aged.
Between males and females males generally have a much greater body
burden of chemicals due to the fact that females are able to secrete much of
the accumulated contaminants through the mammary glands while breast
feeding. There has been little evidence
that race plays much of a role in the degree of body burden, however occupation
seems to present the greatest variation.
Those who work in high exposure environments are much more likely to
have a higher body burden. It does
appear that generations pass contamination down the line causing the next
generation to have a much greater body burden.

Cancer and the Environment

The rate of cancer cases and deaths
overall have been decreasing in the last three decades however what is of great
concern are the types of cancer which have seen increases in the number of
cases and mortality rates. Some have
been linked with exposures, both environmental and occupational, to known
carcinogens. The mortality rates of
breast and gynecological cancer in females, prostate and lung cancer in males,
and colorectal cancer in males and females has declined. The first half of the 1990s saw a two and
half percent decline in cancer deaths, however the rate of decrease has not
nearly kept pace with other advances in medicine such as with heart disease and
stroke considering that a similar amount of resources has been devoted to the
reduction of cancer. Cancer may soon
overtake heart disease as the United State’s number one cause of death. In 1981 Doll and Peto ousted tobacco and diet
as the greatest causes of cancer in the U.S. while occupational and industrial
pollution made up a small percentage.
More recent studies have more or less backed up these claims while also
adding that exposures to electric and magnetic fields and environmental estrogens
may also play an important role.
Exposure to carcinogens in the work place is usually greater than to
those in the community, however community exposure can be much more dramatic as
it includes infants, children, and the elderly who are more susceptible to the
effects. Therefore environmental
regulations are much more strict than workplace related legislation for similar
substances.

Rising temperatures cause glaciers
to shrink, permafrost to thaw, shorter length of ice freeze in river and lake
areas, longer growing seasons, and shifts in plant and animal ranges. As industry continues to contribute more
carbon dioxide, methane, and nitrous oxide to the atmosphere global
temperatures will continue to rise.
Climate change can affect human health both directly and indirectly:
directly such as an extreme increase in temperature could lead to loss of life,
while indirectly change can enable infective parasites to have a greater range
thereby endangering previously unexposed populations. An increase in average temperature will
increase the number of cases of respiratory disorders due to pollution. Temperature increase, rainfall patterns,
concentrations of CO2, pollution levels and more extreme weather events, could
have detrimental effects on agriculture.
These same causes could also limit the species variation and
geographical dominance of American forests.
Extreme and quick climate change could have a very detrimental effect on
ecosystems, especially on the biodiversity of species. Organisms have adapted to the climate over
millions of years, however the speed of the current climatic changes is
virtually instantaneous to evolutionary adaptation. Higher temperatures will result in an
estimated rising of the sea level from .6 to 2 feet over the next century. These higher water levels will result in the
flooding of low lying lands, erosion of beaches, and salt contamination of
water tables. Climate change could
increase the incidences and degree of extreme weather events: less or warmer
cold days and more or warmer hot days, longer more frequent heat waves, more
and lengthier heavy precipitation events, larger areas affected by drought over
longer periods of time, more drastic hurricanes and tropical storms, and an
increase in extreme sea levels would have a very bad affect on agriculture,
human health, industry and society, and water sources.

Readings above may have been drawn from the
following sources:

Six
Modern Plagues and How We are Causing Them, Mark Jerome Walters; Shearwater Books, 2003, ISBN 155963992X